Cam and Head questions - Chevy Impala SS Forum
 
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post #1 of 10 (permalink) Old 01-15-2006, 08:03 PM
Jcope87
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I have a 93 LTZ that is going to get a full rebuild, and I'm trying to decide what way I want to go with it. I'm looking for around 300 HP and 350-400 ft. lbs.

What cam choices am I looking at that will get me this power, while maintaining drivability and emissions compatability?

Also, will the stock head support this much power, or will they need to be ported?

I'm just tossing around ideas now, so any advice you guys have is welcome on the direction I should take this rebuild. I just want a torquey motor that is emissions legal, fun, and runs well at the track every once in a while.
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post #2 of 10 (permalink) Old 01-15-2006, 08:17 PM
96capriceMGR
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You are most deinetely going to have to look at the heads, the TBIs are harder to make work with signifigant cam upgrades so you will have to do more with the heads.
post #3 of 10 (permalink) Old 01-16-2006, 04:05 PM
Daz
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You wouldnt make 300HP with the stock TBI no matter what heads and cam you use.
 
post #4 of 10 (permalink) Old 01-16-2006, 06:43 PM
kdrolt
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Quote:
Originally posted by Jcope87:
I have a 93 LTZ that is going to get a full rebuild, and I'm trying to decide what way I want to go with it. I'm looking for around 300 HP and 350-400 ft.lbs. .... Also, will the stock head support this much power, or will they need to be ported?


Stock heads flow approx 180 cfm intake, so using Vizard's rule-of-thumb the max fwhp would be 8*0.25*180 = 360 fwhp, so in theory yes the heads can make that kind of power.... BUT you would need, at the very least, the LT4 HOT cam to get there... and you would need a lot of ECM chip tuning to make it work.

Ported TBI heads on a 350 have been dyno'd at 313 rwhp and 370+ rw ftlbs (approx 380 fwhp, 420+ fw ftlbs) using a 210 deg cam, if that's enough of a benchmark. Those heads were ported such that the swirl ramp was retained but the edges smoothed and the overall runner and bowl cleaned up in the usual way. The result after porting was on-par with stock iron LT1 heads. You could obtain the same result with new iron L31 Vortec heads but you would also need a Vortec TBI (or carb) intake and then you would have to resize the distrib hole in the manifold (search for the threads/reasons for this). So $500 for L31 heads and $200+ for intake + $? for machine work vs rebuild/porting on stock heads. No matter what you do you will need ECM (chip) work.

The stock TBI itself can flow enough air to make over 330 fwhp but it can't flow enough fuel unless you raise the fuel pressure and use copcar 9C1 TBI injectors OR 454 injectors.

Fast355's posts on Thirdgen.org are the ones you need to read.
post #5 of 10 (permalink) Old 01-17-2006, 02:16 AM
Daz
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IMHO the stock intake manifold wouldnt support it either.
post #6 of 10 (permalink) Old 01-17-2006, 05:46 AM
kdrolt
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Quote:
Originally posted by Daz:
IMHO the stock intake manifold wouldnt support it either.
I used to think that too. Then Fast355 dyno'd 279 rwhp in his G20 van with a 355 TBI v8 using ported 193 swirl port heads. 279 rwhp is over 300 at the flywheel. I do think the stock intake manifold can be improved on (porting it, or use aftermarket) but I don't think its a flow-stopper anymore. And it has the advantage of already being sized for the correct distributor hole for install/removal with the engine + intake still in the car.
post #7 of 10 (permalink) Old 01-17-2006, 05:46 AM
RYS
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kdrolt I have a question for you. When using the Vortec heads is it a good choice to use a stock LT1 cam? How about the LT1 cam with stock heads? What performance gains would we be looking at with just an LT1 cam with stock heads? Thanks.
post #8 of 10 (permalink) Old 01-17-2006, 09:59 AM
kdrolt
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Quote:
Originally posted by RYS:
... When using the Vortec heads is it a good choice to use a stock LT1 cam? How about the LT1 cam with stock heads? What performance gains would we be looking at with just an LT1 cam with stock heads? Thanks.
I don't have Vortec heads so I am not speaking from direct experience with them in a Bcar.

That said, the L31 Vortecs are the Gen 1 clone of the LT1 iron heads.... so the stock Bcar LT1 cam will run great with the Vortecs to the tune of 255-260 fwhp and 330 ftlbs. I say that because the factory stock Bcar LT1 cam was also the factory stock cam used in the L31 engine as used in 1996-1999 Vortec-equipped trucks and vans.

IMO a very conservative approach would be to duplicate what many LT1 owners have done: keep the stock Bcar LT1 cam, modify the exhaust (aftermarket mufflers), and an aftermarket or DIY CAI. That's good for approx 280 fwhp. Ported heads (cleanup on the intake side, and more significant porting on the exhaust side) will gain another 15-20. So you can have 295-300 fwhp using the stock LT1 Bcar cam, and that recipie also holds for using the L31 heads because they're basically the same as iron LT1.

IIRC someone here obtained over 300 rwhp using the above, plus 1.6 stamped rockers, plus "beehive" valvesprings; there is a thread discussing it on the Engine Performance forum if you search. I can't recall if it was Ed R or Karl E. I also don't know if that included ported heads or not. It represents the best you could do while still using the stock Bcar LT1 cam.

So the stock cam can provide bone stock driveability as well as excellent power IF you alter the rest of the engine's breathing. HTH.
post #9 of 10 (permalink) Old 01-17-2006, 12:30 PM
Ram Air 383
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Quote:
Originally posted by kdrolt:
IIRC someone here obtained over 300 rwhp using the above, plus 1.6 stamped rockers, plus "beehive" valvesprings; there is a thread discussing it on the Engine Performance forum if you search. I can't recall if it was Ed R or Karl E.
It was Ed Runnion. However, he has a T56 transmission which allows about 5% more power to the rear wheels.
post #10 of 10 (permalink) Old 01-17-2006, 02:15 PM
kdrolt
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[quote]Originally posted by Ram Air 383:
Quote:
It was Ed Runnion. However, he has a T56 transmission which allows about 5% more power to the rear wheels.
Thanks and agreed.
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